The devastating health consequences of tobacco use result in 5 million deaths/year, making smoking the primary cause of preventable mortality in the world. Susceptibility to nicotine addiction has a heritable component, but while some genetic variants that affect nicotine addiction have been identified, they explain only a fraction of the observed heritability. Indeed, it is clear that in addition to genetic predispositions, environmentl influences play a major role in smoking behavior, most importantly, in the initiation of smoking. The work proposed in this application focuses on the hypothesis that environmental exposures not only affect the people experiencing them, but can also have a heritable effect on nicotine-relate behaviors in children. Specifically, epigenetic information can carry environmental information between generations. For example, epidemiological evidence in humans suggests that parental diet and smoking history can affect cardiovascular disease risk in their children. In addition, adolescents whose parents smoke are more likely to smoke themselves and also initiate smoking at an earlier age, although the mechanism underlying this association is unknown. In multiple contexts, is becoming increasingly clear that understanding the effects of ancestral food and drug exposure on offspring metabolism and behavior will be required for a detailed understanding of disease susceptibility. In other words, many diseases with complex genetic bases may also be subject to confounding epigenetic effects in addition to the long sought after genetic predispositions. We recently demonstrated that, in rodents, paternal diet affects metabolic gene expression in offspring. Thus, it is conceivable that paternal exposure to nicotine, the addictive component of tobacco smoke, may have transgenerational effects on gene expression that ultimately affect metabolism and dependence- related behavior. Indeed, in this proposal we provide preliminary evidence that male mice exposed to nicotine father offspring with altered gene expression in the liver and in key brain regions involved in nicotine dependence. We propose to comprehensively characterize this effect from molecular changes in fathers' sperm induced by nicotine, to gross effects on nicotine-related behaviors in children. Together, these experiments constitute an extensive characterization of a novel pathway linking nicotine exposure to phenotype across generations. These results will likely have important implications for the epidemiology of complex diseases in humans.